FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in accordance with the prior art. Wireless telecommunications system 100 comprises: wireless terminal 101, base stations 102-1, 102-2, and 102-3, and wireless switching center 111, interconnected as shown. Wireless telecommunications system 100 provides wireless telecommunications service to all of geographic region 120, in well-known fashion.
The salient advantage of wireless telecommunications over wireline telecommunications is the mobility that is afforded to the users of the wireless telecommunications system. On the other hand, the salient disadvantage of wireless telecommunications lies in that fact that because the user is mobile, an interested party might not be able to readily ascertain the location of the user.
Such interested parties might include both the user of the wireless terminal and remote parties. There are a variety of reasons why the user of a wireless terminal might be interested in knowing his or her own location. For example, the user might be interested in telling a remote party where he or she is.
There are a variety of reasons why a remote party might be interested in knowing the location of the user. For example, the recipient of a 911 emergency call from a wireless terminal might be interested in knowing the location of the wireless terminal so that emergency services vehicles can be dispatched to that location.
A variety of techniques are known in the prior art for estimating the location of a wireless terminal.
In accordance with one technique, the location of a wireless terminal is estimated to be at the center of the cell in which the wireless terminal is located. This technique is advantageous in that it does not require that additional hardware be added to the wireless terminal or to the wireless telecommunications system, and this means that the first technique can be inexpensively implemented in legacy systems. The first technique is only accurate, however, to a few kilometers, and, therefore, it is generally not acceptable for applications (e.g., emergency services dispatch, etc.) that require higher accuracy.
In accordance with a second technique, the location of a wireless terminal is estimated by triangulating the angle of arrival or the time of arrival of the signals transmitted by the wireless terminal to be located at various receivers. This technique is accurate to within a few hundreds of meters and is advantageous in that it can be used with legacy wireless terminals. It is disadvantageous, however, in that it generally requires that hardware be added to the telecommunication system's base stations, and this is very expensive.
In accordance with a third technique, the location of a wireless terminal is estimated by a radio navigation unit, such as a Global Positioning System (GPS) receiver, that is incorporated into the wireless terminal. This technique is accurate to within tens of meters and is advantageous in that it does not require that additional hardware be added to the telecommunication system's infrastructure. Two disadvantages of GPS, however, is that it cannot be used with legacy wireless terminals that do not comprise a radio navigation unit, and it often fails to work indoors.
In some instances it might be desirable to know whether a wireless terminal is located indoors. In some such instances, such as when emergency parties are dispatched to a distressed caller, it might be desirable to have this information in addition to an estimate of the location of the wireless terminal—particularly when the estimate is imprecise—while in some other instances this information might be sufficiently useful without a location estimate.
Naturally if there is a mechanism for obtaining an accurate estimate of the location of a wireless terminal (e.g., Global Positioning System [GPS], etc.) and the geographical boundaries of buildings are known, then it is a straightforward matter to determine whether the wireless terminal is indoors or outdoors. However, information about the locations of buildings might not always be available. Moreover, a wireless terminal might lack the hardware or software required for obtaining an accurate location estimate. Finally, even when a wireless terminal does in fact have the requisite hardware and software, location estimation techniques such as GPS and triangulation can work poorly when the wireless terminal is indoors, due to signal penetration loss.
What is needed, therefore, is a technique for estimating whether a wireless terminal is indoors that is capable of overcoming these difficulties.